1. Field of the Invention
The present invention relates to dry silver photothermographic imaging materials and to stabilizers for alkyl ketazine leuco dyes used in color photothermographic imaging systems.
2. Prior Art
Photosensitive, heat-developable, dry silver sheet materials, as described for example in U.S. Pat. Nos. 3,457,075 and 3,839,049, contain a photosensitive silver halide catalyst-forming means in catalytic proximity with a heat sensitive combination of a light stable organic silver compound and a reducing agent therefor. When struck by light, the silver halide catalyst-forming means produces silver nuclei which serve to catalyze the reduction of the organic silver compound, e.g., silver behenate, by the reducing agent at elevated temperatures. To improve the image density and color it has been found desirable to iinclude toners in the sheet construction.
Color photothermographic imaging systems have been described in patent literature. U.S. Pat. No. 3,531,286 describes a system using paraphenylenediamine and photographic color couplers. U.S. Pat. No. 3,985,565 discloses the use of phenolic leuco dye reducing agents to reduce the silver and provide a color image. U.S. Pat. No. 4,460,681 discloses a multilayer color photothermographic system using a variety of leuco dyes separated by barrier layers.
U.S. Pat. No. 4,587,211 describes the use of poly(vinyl chloride) and poly(vinylidene chloride) polymers as stabilizers for the dye image formed by oxidation of syringaldazine leuco dyes.